Electrophoresis is the translation of charged objects in a fluid in response to an electric field. Electrophoretic inks are useful as a medium to enable bistable, low power types of displays. Electrophoretic displays have been developed using a dyed fluid and white particles sandwiched between parallel electrodes on top and bottom substrates. When an electric field is applied transverse to the substrates across the dyed fluid to translate the white particles to the viewing surface, the display appears white. When the electric field is reversed to translate the white particles away from the viewing surface, the display appears the color of the dyed fluid. Similarly, electrophoretic displays have also been developed using a clear fluid with two differently colored particles of opposite charge (e.g., positively charged white particles and negatively charged black particles) sandwiched between parallel electrodes on top and bottom substrates. When the electrode on the viewing side is charged negatively, the positively charged white particles are translated to the viewing surface, and the display appears white. When the electrode on the viewing side is charged positively, the negatively charged black particles are translated to the viewing surface, and the display appears black. Conventional electrophoretic architectures typically use electrodes that are electrically insulated from the colorant particles and the carrier fluid such that there is no significant steady state current flow. The prior embodiments using parallel electrodes to translate particles transverse to the top and bottom substrates do not enable a transparent state. When the top surface is color A, then the bottom surface will appear color B, and vice versa.
A transparent state can be enabled by “in-plane” electrophoretic displays, in which electrodes are arranged to apply electric fields that are substantially parallel to the substrates to translate colorant particles through a clear fluid parallel to the substrates. This allows the colorant particles to be collected out of the viewing area of the display to create a transparent state. The colorant particles can also be spread across the viewing area of the display to create a colored state. Since the travel distances required for in-plane electrophoretic displays are typically much larger, the switching speeds are typically much slower. Reducing the travel distance has the undesired effect of reducing the clear aperture of the viewing area for a given electrode width. Such an architecture requires electrical cross-over of in-plane electrodes that increases manufacturing complexity.
For the reasons stated above and for other reasons that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternate ways to control colorant particles in an optical display.